The invention relates to a cover for a secondary part of an electrical linear motor, wherein the secondary part comprises at least one first and one second secondary part element, and wherein each secondary part element has a toothed profile. The invention also relates to a secondary part having a cover, and to a linear motor having a secondary part and a cover.
Electrical machines have a primary part and a secondary part. By way of example, the secondary part is a rotor of a rotary electrical machine or else a moving part of a linear motor. By way of example, the primary part is a stator or a stationary part with a single-phase or polyphase winding. In the case of linear motors, both the primary part and the secondary part may be moving parts.
In general, stators and rotors for electrical machines have a laminated core, comprising individual electrical laminates, wherein the winding or else permanent magnets for generation of magnetic fields is or are arranged on the laminated core. The individual laminates for stators and rotors are generally stamped individually and are joined together to form laminated cores, for example by stamping and packeting, welding or bracketing.
In order to guide the main magnetic flux between a stator and a rotor, toothed laminates are normally used in stators/rotors that are fitted with windings. The winding is arranged in the slots in the laminates and the laminated core. After the insulation of the slots, the winding is introduced, for example by drawing it in.
DE 10 2004 045 992 A1 discloses an electrical machine whose secondary part has no active means, such as windings through which a current can be passed or permanent magnets, for producing a magnetic field. In the case of a permanent-magnet synchronous linear motor with a secondary part without any permanent magnets, the primary part has windings through which a current can be passed and has permanent magnets, wherein the secondary part has only a toothed structure composed of a material which contains iron.
WO 2006/032255 A1 discloses a secondary part for an electrical linear motor, wherein the secondary part has no active means for generation of magnetic fields. Various embodiments are specified for a passive secondary part such as this.
Linear motors such as these are used in various fields of engineering as drives, in particular direct drives, for example for machine tools, processing machines such as automatic drilling, milling, turning, placement or bonding machines.
The physical length of the movement path depends on the purpose of the linear motor, and must be at least as long as the required movement distance plus the length of the rotor. In order to be flexible for the design of linear motors of different length, the secondary parts are, for example, formed from relatively short secondary part elements, which are arranged in a row to form the desired length.
The butt joints which are used in this case are, however, disadvantageous, particularly in severe operating conditions, in that dust, operating liquids, aggressive substances, etc. can accumulate in them. It is also impossible to prevent dirt and operating liquids, solid parts, tool pieces, etc. being deposited on the movement path. These foreign objects then, in particular, enter the air gap in the linear motor, thus enormously adversely affecting the life of the linear motor. Particularly in the case of movement paths which are arranged horizontally, it is impossible to prevent accumulation of dirt. Even if there is little dirt, it is only a question of time as to when the linear motor will fail.